Detailed knowledge of the processes involved in the regeneration of the neuromuscular junction is basic to our understanding of how nerve-muscle function is restored after trauma. It may also give insights into the mechanisms of synapse development in the embryo. During this project's initial term we examined regenerating neuromuscular junctions of the frog. After nerve damage, regenerating axons unerringly reinnervate original synaptic sites on the myofibers. We devised a way to remove the myofibers as well as nerve leaving in tact the myofibers basal lamina sheath, the Schwann cell which normally caps the nerve terminal, and the Schwann cell's basal lamina. An analysis of reinnervation in the absence of the myofiber indicated that the Schwann cell and/or the basal laminae guide axons to the original synaptic sites. It also revealed that factors stably maintained in the myofibers' basal lamina trigger the axon terminals' morphological differentiation. Regenerating myofibers form inside the basal lamina sheaths of the original myofibers. Our studies showed that factors provided by denervated synaptic sites on the basal lamina organize ACh receptors in the new myofibers' membrane. Our objectives for the next five years are: (1) To examine the role of the Schwann cell, and the basal laminae of the muscle and Schwann cell in precise reinnervation of original synaptic sites in muscle; (2) to further characterize the influence of components of the denervated synaptic site on differentiation of regenerating nerve terminals in the absence of the muscle cell with particular emphasis on acetylcholine synthesis and release and the terminals' stability; (3) to determine the influence of components of denervated synaptic sites on the organization of acetylcholine receptors in regenerating muscle fibers. For these studies we plan to use a variety of surgical, light and electron microscopical, electrophysiological and biochemical techniques.